1. Field of the Invention
The present invention relates to a sheet material identification apparatus to identify the difference in skin friction resistance of objects to be measured and the difference in surface roughness as well as the difference in surface material, both to be the cause thereof and a heating apparatus as well as image forming apparatus such as printers in electro photography system, photocopiers, ink jet printers, thermal head printers, dot impact printers, facsimiles, and compound devices comprising them, etc. equipped with this apparatus.
2. Related Background Art
Conventionally, a image forming apparatus of any kind is generally an apparatus to form an image on sheet state recording material such as plastic type film plate for plain paper, postcard, cardboard, letter paper and OHP, and printers, photocopiers and facsimiles, all adopting an electro photography system, as representative examples thereof, form a toner image on recording material by electrostatic image forming means using toner as developer and thereafter heat and press the recording material with fixing means to bring the toner image into fusion and fixation for image forming.
In addition, the other apparatuses such as printers, photocopiers, facsimiles and the like, all adopting ink-jet system, use ink as developer to implement image forming onto recording material with image forming means which makes use of mechanical or thermal reaction to bring a recording head configured with a number of nozzle having micro orifice into rapid discharge of ink.
Moreover, the other apparatuses such as printers, photocopiers, facsimiles, and the like adopting the thermal transfer system use ink ribbons as developer and use thermal head to bring ink into heat transfer from the ink ribbon with image forming means to form image onto recording material.
Incidentally, these apparatuses have undergone improvements in recent years, and devices for enhancement in image quality improvement and in speeding up of process speed have been being realized with various means, and at the same time, cost-saving measures have been devised to advance price discount giving rise to popularization.
However, there are various kinds of recording material for use in these image forming apparatus including plain paper, high quality paper which has undergone special surface treatment for envelopes and a sheet for OHP made of resin, etc., moreover all of which have been being used all over the world accompanied by proliferation of the apparatus, therefore giving rise to necessity to correspond with the order for feasibility of forming good images for any recording material used in respective locations, and especially, roughness on the surface of recording material which significantly affects image forming conditions is very important element.
For example, in the apparatus adopting electro photography system, in case of the surface of the recording material for use being smooth (hereafter to be referred to as smooth sheet) and in case of being rough (hereafter to be referred to as rough sheet), in the fixing part, heating efficiency of transferring heat from a heating source to the sheet surface is different in accordance with the difference in thermal resistance due to difference in surface property, and fixing a rough sheet is brought into fixing under a fixing temperature which is appropriate for a smooth sheet will end in introducing insufficient fixing, and therefore it is necessary to bring a rough sheet into fixing under higher temperature. Therefore, for an apparatus under the present state, a temperature under which a rough sheet can be brought into fixing is used as a fixing temperature while a smooth sheet is always continued to be brought into fixing under excessive temperature, and for a rougher sheet, higher fixing temperature is required, and therefore at the time when such a sheet is used, a selection mode was provided to make a user change the setting of the fixing temperature.
As a particular example, basic configuration of a printer adopting an electro photography system is shown in FIG. 6.
That is, FIG. 6 is a sectional view of major parts of a conventional printer, and in the printer, the surface of a photosensitive drum 2 is brought into charging to a predetermined polarity uniformly with a charging roller 1, and thereafter only the region that has undergone exposure by means of an exposing means 3 such as laser, etc. is deprived of charge so that a latent image is formed on the photosensitive drum 2. Thereafter, this latent image is developed with toner 5 of a developing device 4 to be visualized as a toner image. That is, the toner 5 of the developing device 4 is brought into friction charging between a developing blade 4a and a developing sleeve 4b to the same polarity as the charged surface of the photosensitive drum 2, and DC and AC biases are applied in an overlapped fashion to the developing gap part where the photosensitive drum 2 and the developing sleeve 4b faces each other to bring the toner 5 into floating and oscillating while selectively attached to the latent image forming part of the photosensitive drum 2 in operation of the electric field, and thereafter this toner 5 is conveyed with rotation of the photosensitive drum 2 to the transfer nip part formed by the transfer roller 6 and the photosensitive drum 2.
On the other hand, as for the recording material 7 such as paper etc. where an image is recorded, the tip part is brought into sheet feeding through any of the following routes, namely, from the recording material housing box 7a to reach a pair of vertical conveyance rollers 7d with a pair of a pair of sheet feeding rollers 7c (the bottom roller may be a pad), and thereafter is conveyed by this pair of vertical conveyance rollers 7d to reach pre-transfer rollers 7d′ or is conveyed by the pair of sheet feeding rollers 7c from a manual sheet supplying tray 7b to reach the pre-transfer conveyance roller 7d′, and moreover is conveyed by these pre-transfer rollers 7d′ along the spacing between the transfer top guide plate 9 and the transfer bottom guide plate 9′ with predefined incident angle to reach the transfer nip part. Up to the point when the recording material 7 is conveyed from these pre-transfer conveyance rollers 7d′ to the transfer nip part, the recording material 7 may be charged on the surface by sliding with a various kinds of members which the recording material 7 has contacted before it is conveyed to reach this region, and therefore, neutralization brush 8 for removing such unnecessary charging which will result in image confusion at the time when electrostatic recording is implemented is provided so as to come in contact with the back surface side of the recording material 7 during conveyance and be grounded.
In the transfer part, in order to electrostaticly attract and relocate the toner 5 on the photosensitive drum 2 to the recording material 7 side, a high voltage with the opposite polarity of the toner 5 is applied to the transfer roller 6 on the back surface of the recording material 7, the toner 5 is electrostaticly attracted to the rear surface of the recording material 7 so that a toner image is transferred onto the recording material 7 and the rear surface of the recording material 7 is charged to the opposite polarity of the toner 5 and the transfer charge for continuing to hold the transferred toner 5 is given to the rear surface of the recording material 7.
Lastly, the recording material 7 where the toner image has been transferred is conveyed to reach a fixing device 12 configured by comprising a pressure roller 14 to form a nip part with the heat rotation body 13, and is heated and pressed in a nip part by a heater provided in the heating rotation body 13 side so as to keep the fixing temperature set in advance and then a toner image is fixed.
Here, since extraneous attachment such as toner and the like having different polarity remains on the surface of the photosensitive drum 2 after toner image transfer, the surface of the photosensitive drum 2 after passing the transfer nip part is cleaned in a cleaning device 10 with a cleaning blade 10a which comes in counter contact with the surface of the photosensitive drum 2 so that the extraneous attachment is removed, and will readily wait for the next image forming.
Here, since the above described respective configuring elements of the charging roller, the photosensitive drum, developing device and the cleaning device have short exchange cycle, an apparatus in a cartridge exchange system which enables to exchange in a unit of a cartridge 11 where these items are integrated has mainly come into wide use.
Among the above described steps, as an image fixing system, a fixing apparatus in contact heating type with good heat efficiency and safetiness is widely known, conventionally, a heat roller fixing apparatus has been used and is configured by pressing and bringing in contact a heat fixing roller having mold-releasing layer formed on a metal core of a metal cylinder enclosing a halogen heater inside the cylinder and a pressure roller configured by forming an elastic layer made of a heat resisting rubber on a metal core and forming on the surface thereof a pressing side mold-releasing layer, in recent years, as a further more heating efficient system, a film heating type fixing device using in stead of the above described heat fixing roller a fixing film with a heat-resisting resin film with low heat capacity being processed to shape a cylinder and to form a mold-releasing layer so that from inside of the fixing nip part of this film a ceramic heater is brought into contact to heat.
This kind of film heating type fixing device has higher heat transfer efficiency compared with a heat roller system using as a fixing roller a metal cylinder enclosing a conventional halogen heater in view of recent promotion of energy saving, and attracts attention as a system with fast startup of the apparatus and has been adopted in faster machines, but particularly in this system, since heating speed is regarded important, the heat capacity on the heating surface of the fixing part needs to become small, and consequently it is difficult to form an elastic layer on the heating surface and hard heating surface is being used. Thus, this kind of fixing system is configured to easily give rise to a difference in heating efficiency due to a difference in irregularities on the recording material surface.
In the respective kinds of image forming apparatuses using such a fixing device, accompanied by the above described speeding trend in processing speed, difference in types of paper gives rise to a problem of remarkable difference in fixing performance, and it is necessary for a user himself to input into a printer an appropriate fixing mode in advance corresponding with types of paper for use by the user.
However, to force a user to select modes in order to switch the fixing conditions like this depending on types of paper for use each time would increase user's work load and in case of wrong selection mode, fixing performance for that printing would get insufficient or otherwise overheating would waste power and cause image deficiency due to heat offset or possibly might introduce toner pollution of the fixing device.
In addition, as in recent years, under a circumstance of use where a plurality of users share a network printer, one user uses special paper and switches the mode setting corresponding with that, and thereafter he might leave that special paper in the apparatus, and therefore when another user who does not know about it uses the printer, the mode does not correspond and appropriate fixing is not implemented, which may highly possibly end in giving rise to the above described problem.
In addition, with regard to the number of fixing modes available for setting, there are various levels in smoothness of actual paper in strict terms, and it is impossible to provide optimum conditions for them respectively, and therefore the number of setting mode is limited by fixing sheets having a certain range of smoothness at a same mode collectively, and for a special sheet, there is a case where the power more than necessity is used for fixing, and there is a case where inefficient fixing is implemented depending on the combination between paper and setting.
On the other hand, in such an apparatus that adopts the above described ink-jet system, required quantity of ink is different in case of smooth sheet being the recording material for use and in case of rough sheet, and when a rough sheet undergoes image forming with a quantity of ink which is appropriate for a smooth sheet, the ink penetrates in the direction of the thickness of the sheet to introduce insufficient density, and therefore more ink is required to be ejected for a rough sheet. In apparatuses under the present circumstances, this requires a user to operate a printer to identify that type of paper in advance for sheets with these different surface properties.
In addition, in such an apparatus that adopts the heat transfer system, required amount of power is different in case of smooth sheet being the recording material for use and in case of rough sheet, and when a rough sheet undergoes heat transfer with a quantity of power which is appropriate for a smooth sheet, the heat resistance is large to drop transfer property of the ink to introduce insufficient density.
As described above, any of the present apparatuses will consume excess temperature, ink and power for preventing decrease in image quality of an image due to surface roughness of recording material or otherwise introduce decrease in image quality, and in order to prevent these problems, it is necessary to switch these conditions corresponding with surface roughness of recording material, but under the present circumstances, only such a method to force a user to operate to switch settings or optical sensors which require complicated configurations or signal processing used in a part of apparatus are taken into consideration, only introducing a significant cost increase.
Therefore, several apparatuses to implement image forming by detecting surface roughness of recording material and changing image forming conditions corresponding with the detected result thereof have been proposed so far, and among them, a detection principle enabling surface roughness of recording material to be detected comparatively inexpensively and rapidly has been proposed. These proposals have disclosed a method of detecting physical phenomena such as oscillation, sliding sound and the like taking place due to sliding when the contact means brought into contact with the surface of recording material slides on the surface of recording material and detecting the difference in those detection quantities as difference in surface roughness, and as a particular configuration, such a configuration has been proposed that provides the contact means with a piezoelectric element to detect oscillation which is converted to electric signals.
However, particular configuration conditions required for a member (hereinafter referred to as a probe) actually to be brought into contact with the surface of recording material are not disclosed in detail in the above described proposal, and only such a configuration with a simple straight line probe having one end part fixed in the upstream side in the conveyance direction and having the tip in the downstream side brought into contact not to go askew from the conveyance direction has been shown, and it was difficult to actually realize highly accurate detection with this content.
Therefore, in order to spectacularly improve sheet material identification performance in a detection system using a piezoelectric element and make it available for common use, the present inventor studied shape and mounting configuration of a sensor probe newly; found that very high identification performance is obtainable by giving to the tip part of the probe such construction to make the tip contact part enable to oscillate forward and backward in the conveyance direction on the conveyance plane and setting an angle so that the tip contact part protrudes into the surface to be measured in disagreeing with the conveyance direction; devised an S-shaped surface detecting sensor 15 configured by comprising a probe being a rectangular metal plate subject to bending twice to be S-shaped in side view as shown in FIGS. 7A and 7B, which is rotationally fixed into the rotation shaft, as a configuration to realize such a structure most inexpensively without disturbing sheet conveyance; mounted this sensor onto the transfer top guide 9 shown in FIG. 6 as optimum location to enable detection from the sheet surface side in the downstream side of the sheet conveyance direction in the interflow part of both of two sheet conveyance routes, that is, one from a paper cassette and the other from a manual sheet supply tray, enabling detection in any case of sheet feeding, to assess; and consequently confirmed that very high identification performance is obtainable without disturbing sheet conveyance.
As shown in FIG. 7A in further detail, this sensor has an S-shaped probe 15a with a piezoelectric element part 15b formed in the flat part being fixed onto a probe holder 15c with a fixing screw 15d at its non-conveyance side end part, and this probe holder 15c is fixed rotatably onto a probe rotation shaft 15e having axis direction perpendicular to the conveyance direction and in a parallel direction to the conveyance plain, and the probe tip part is brought into pressure contact by not shown pressure means at the contact pressure around 10 to 31 g to the conveyance plain with this probe rotation shaft 15e as the center. Moreover, this probe rotation shaft 15e is fixed on a sensor holding plate 15g (=transfer top guide) through a shaft receiver 15f, and as the conveyance plain, a conveyance plain plate 15h (=transfer bottom guide plate) is provided on the sheet conveyance lane. FIG. 7B is to show the relationship of dispositions of respective members in case of top view of these configuring members, in the center of the sensor holding plate 15g, an angled opening is provided for bringing the tip part of the S-shaped surface detecting sensor 15 into contact with the conveyance plain, and from the surface of the piezoelectric element part 15b and the surface of the metal plate of the S-shaped probe 15a, soldered signal leads for picking up detection signals are pulled out along the longitudinal direction on the surface of the sensor holding plate 15g to reach the electric part.
FIG. 8A shows a result of measuring output signal wave form of a sensor when an S-shaped surface detecting sensor configured as described above is used and major sheets of paper used in an actual printer in electro photography system are brought into sheet feeding in succession, and therein the horizontal axis is for type of paper and the vertical axis is for signal voltage. In this measurement, as the order of sheets brought into sheet feeding, a rough sheet and a smooth sheets are arranged in turn and fed, and in the measurement result, the detected signal levels for rough sheets are classified to be high and the signal levels for smooth sheets low.
However, this result itself only provides signals coming out of respective sheets in collected wave forms of minute pulse signals, and therefore, it is necessary to process to pick up signals rapidly with good timings, and there is a case where a high pulse signal occurs due to unpredicted cause in a part of sheets locally, though, among signal wave forms of smooth sheets which originally is supposed to give rise to low signals, and in order to make the apparatus internally identify the detection results accurately, the wave forms as they are were not appropriate. Accordingly, as a signal processing method further appropriate to this sensor, the present inventor provided the latter step of the signal detecting circuit with an integral circuit; devised moreover a signal processing circuit to devise so as to implement self-discharge appropriately; and processed the above described pulse signals; and consequently, wave forms as shown in FIG. 8B were obtainable, making identification of types of paper readily realizable.
Moreover as an application of the present sensor, a flexure structure 16 is provided in the conveyance path of sheet material as shown in FIG. 7C so as to configure to readily form paper loop in the contact locations where the sensor contacts the sheet material, giving rise to difference in height of this loop according to difference in rigidity, that is, in terms of sheet thickness or replacing difference in rigidity with the quality of material being same, difference in shape of sheets during conveyance for thin sheet 7′ and a thick sheet 7″ as in the drawing; introducing difference in pressure so as to lift up the probe tip part upward from downward accompanied by difference in quantity of loop deform of sheet to relatively shift the contact pressure applied to the probe tip part of the sensor; and consequently enabling to detect difference in rigidity of paper (higher rigidity gives higher signal level), and making realizable detection of thickness of sheet material since difference in rigidity between those with the same quality of material is proportional to thickness of sheet material.
Appropriately implementing signal processing with such a configured and mounted S-shaped surface detecting sensor 15 as described above, detection of surface property, rigidity/thickness of paper conveyed in is completed at least prior to the fixing step so as to enable fixing controls to be switched, a user will be able to use the apparatus without taking care about types of paper for use and without introducing image defects or unnecessary power consumption.
However, the above described configuration presented good identification performance and sheet conveyance performance for the level of basic study, but when this S-shaped surface detecting sensor was actually incorporated inside an apparatus to implement consecutive sheet feeding endurance tests, there existed still imperfect parts for use for a long period. FIG. 9 is to show detects taking place in actual use, with the above described sensor having been incorporated inside a printer, and a graph of assessment result on detection characteristics of a sensor when consecutive sheet feeding endurance tests were implemented regularly in 50000 sheets to reach 450000 sheets with standard paper.
For the detection characteristics assessment of the sensor, ten kinds of paper with representative rough sheets and smooth sheets taken from major types of paper used for a printer in a commingled fashion were used and conveyed, and among identification symbols for types of paper, characters respectively stand for F: smooth paper, R: rough paper having uniform surface roughness and W: rough paper subject to wave form modification onto the paper surface, and numerals respectively stand for basic weight of each paper, and in general, paper with larger basic weight gives higher rigidity and thickness becomes thicker at the same time. In addition, OHT denotes an OHP sheet with surface being very smooth, and a sheet in this level will be referred to as super smooth sheet.
As understood from the endurance result in FIG. 9, at each checking point of time from the start to sheet feeding in the amount of 450000 sheets and afterwards, detection performance of the present sensor gave rise to difference in detection signal levels for respective sheets so as to enable respective types of paper to be categorized into three kinds of “super smooth sheet, smooth paper, rough paper and thick paper (basic weight of not less than 135 g), and identification by providing respective regions of “types falling between the super smooth sheet and the smooth paper” and “types falling among smooth paper and rough paper and thick paper” with threshold values is feasible, and identification performance itself is maintained, but in case of considering a threshold values for respective regions throughout the entire endurance period, the threshold value for “types falling between the super smooth sheet and the smooth paper” may always remain at a constant threshold value (the value around 0.7 V in this example), but there is little margin in the region of “types falling among smooth paper and rough paper and thick paper”, and between the value of the detection with respect to F105 at the point of time of 50k and other values which were detected to comparatively low levels in the rough paper and the thick paper at other endurance point of time there are cases with approximately the same level or with reversal, it is difficult to identify each region with one threshold throughout the entire endurance period, and for some point of time of use, there exists a risk of misdetection taking place between some parts of sheets.
In addition, in the above described endurance assessment, fluctuations in detection signal level for thick paper with comparatively large basic weight tend to get large, and as an application of sheet material identification apparatus, among image forming apparatuses in the same electro photography system, in case of a color machine which brings tone images consisting of a plurality of color toner layers into fixing at the same time, or a rapid machine which implements fixing very rapidly, such a system in which a fixing roller surface of the first part of the fixing device is configured by an elastic layer of heat-resisting rubber and the sheet material surface is enclosed with a soft surface so as to increase heating efficiency is mainly adopted, and in such an apparatus, changes in fixing performance due to difference in heat capacity will be more important than difference in more or less roughness on sheet material surfaces and therefore reliability on identification capability on rigidity of paper or thickness of paper both of which are highly correlational to heat capacity of sheet material might become a problem.